A well-known problem in relation to screening devices of the above mentioned type lies in the risk of the screening body of the screening device sagging and/or wrinkling during operation. If the screening body of the screening device is caused to sag and/or wrinkle during operation there is a risk of the screening body getting damaged or getting stuck. This in turn may damage or jam the driving mechanism. Furthermore, the appearance of the screening device in the fully extended position may become aesthetically un-pleasing for the user. In screening devices operated by means of an electric motor it is therefore essential that the control system is enabled to determine and/or detect the fully extended position of the screening body of the screening device.
In the prior art, various methods have been suggested in an attempt of alleviating the above problem. For instance, EP 3 121 364 A1 describes a method for controlling a driving unit of a roller shutter in which a learning process is employed in order to enable the controller to detect the fully extended position and the fully retracted position of the screening body. In the learning process the controller drives the screening body between its fully extended position and its fully retracted position a predetermined number of times, such as four times, and in doing so detects when a threshold of for instance a torque or an intensity of the current drawn by the electric motor driving the screening body is exceeded within a predetermined time span and registers the corresponding position of the screening body. The position of the screening body may, for instance, be defined as a number of revolutions of the roller tube of the screening device.
However, the prior art methods have the drawback of being excessively cumbersome and time consuming to perform. Furthermore, the prior art methods pose a significant risk of inaccurate detection of the fully extended position of the screening body. Therefore, in the prior art methods, a risk of sagging and/or wrinkling of the screening body of the screening device in the fully extended position is nevertheless still occurring, and in consequence the screening body may still wrinkle or get stuck.
Thus, there is a desire to propose an improved method of the type mentioned by way of introduction, with which the above drawbacks are more fully alleviated.